Process and apparatus for the separation of solid materials of different specific gravities



1,811,026 PROCESS AND APPARATUS FOR THE SEPARATION OF SOLID June 23, 1931. G. RAW

MATERIALS OF DIFFERENT SPECIFIC GRAVITIES 27, 1928 2 Sheets-Sheet 1 Filed Sept.

June 23, 1931. W 1,81 1,026

PROCESS AND APPARATUS FOR THE SEPARATION OF SOLID MATERIALS OF DIFFERENT SPECIFIC GRAVITIES Filed Sept. 27, 1928 2 Sheets-Sheet 2 Patented June 23, 1931 UNITED STATES PATENT OFFICE GEORGE RAW, OF WASHINGTON, ENGLAND rnocEss AND AF ARATUs FoR THE SEPARATION OF SOLID MATERIALS OF DIFFERENT SPECIFIC GRAVITIES Application filed September 27, 1928, Serial No. 308,787, and in Great Britain October 28, 1927.

I This invention comprises improvements in and connected with the separation of solid materials of diflerent specific gravities by making use of the pressure of air or other gaseous fluid, applied to the materials in a bed or mass on a pervious support, so as to distend or attenuate the bed and cause stratification of the materials according to their densities. The invention is particularly applicable for the cleaning ofcoal from stone and inferior coal but may be applied in other cases where dry separation of materials is desired, for example, the dry separation of ores from their gangue,

' An important obJectof the invention is to enhance or improve the levitating effect on In that speclfieation it was shown that a t very advantageous levitating effect on a bed or mass of unsized materials of' different specific gravities "could be attained by the employment of pulsating or fluctuating static pneumatic pressure conditions in the bed, the application of these conditions with suflicient' rapidity of the pulsations giving a more effective Stratification of the materials than a uniformly applied pressure, resulting-in a higher order of fluidity or distension of the bed andobviating risk ofpiping of the gaseous medium through the bed. It thus follows that any improvement of the pulsating-pressure conditions will be in the direction of still further improving the stratifying action.

A study tions in the air apparatus already employed by me in accordance with my said, prior patent application, revealed that thecharacter of the fluctuations of pressure was in accordance with the laws of sound waves. From this it will be'underof the pulsating pneumatic condibox or pneumatic chamber of the pulsator causes a wave of condensation to be generated at the pulsator port which wave is propagated along the length of the airbox with the speed of sound followed by a rarefaction in accordance with Well-known principles.

The wave thus generated is reflected from any surface it meets, in a direction determined by the angle which the reflecting surface makes with the line of propagation-of the wave. However, if the air box or chamber be made rectangular in the direction of travel of the wave, so that the wall of the box opposite the pulsator is plane and perpendicular to such direction, then the reflected wave will returndirectly to the pulsator, and will there be reflected again and will repeat this course as before. In such an air box, if a single impulse be applied, the wave will travel backwards, and forwards along the length of the air box until it is damped out by. the viscosity of the air and other frictional losses, but if the impulses be periodically applied at such frequency that each one can be timed to coincide with the return of the wave generated by the previous impulse, this wave will be reinforced and again traverse the air box with increased amplitude due to .the superimposition of the one wave upon the other. In this way a condition of resonance may be established in air chamber. Obviously, if the air box be of inappropriate shape, and particularly if the wall opposite to the pulsator be not at right angles to the axis of the wave, or not a plane surface, the waves will not be reflected directly backwards and forwards, but wouldbecome confused and make satisfactory reinforcement impossible.

From the considerations thus set forth it fluctuations of pressure of considerable amplitude and high frequency in the air box. Experiments haveshown that the Stratification of the materials responds very sensitively to this increased amplitude of fluctuating pressure and that there results a materially improved distension or fluidity of the bed of will be understood that it is possible to set up comprising a superimposition of-pressure waves one upon another in synchronism, one wave being amplified by the super-imposition of another so as thereby to build up fluctuating pressure conditions'in which the amplitude of vibration or range of pressure variation is as great as possible. In actual practice it has been found possible in this way to attain a high degree of resonance.

If it be not desired to apply the pulsations with a frequency as high as that of the oscillations of the air in the air box, the reinforcement or amplification may be made to take place on the second or some successive return of a wave, provided that each impulse is timed to meet a wave at the moment of its selected return to the pulsator. In this case, the amplitude of the fluctuation of pressure would not, of course, be maintained through the cycle at so great a level, as it would in the case of the reinforcement of every returning wave. There would obviously be successive reductions in amplitude at each reflection be tween one reinforcement and the next. Nevertheless, a very eflicient stratifying effect is obtainable under these conditions.

In order to establish the conditions above described, separating apparatus in accordance with the invention comprises an air box fwhich is as closely as possible rectangular in the direction of travel of the compression waves, is of uniform cross-section, and has its far end opposite the pulsator of plane form and disposed at right angles to the said direction of travel so as to enable the latter to be reflected back to the pulsator:-without undue deflection or distortiomand the length of the box is so related to the frequency of pulsation that the impulses will he periodically applied at precisely the right moments to reinforce the reflected waves'in the air box on their returns to the source of generation. When apply ng the inventlon in connection with apparatus as disclosed in my prior patent specification aforesaid, the air box would be modified or constructed to satisfy these rc quirements.

It is important that the operation of the pulsator device be correctly timed. If the timing were incorrect, the impulses delivered by the pulsator would be placed out of synchronism with the'arrival of a reflected wave at the pulsator and reinforcement of the wave would not occur. On the contrary the maximum amplitude of any wave would be that due to a single impulseand eachwave would, therefore, die out after a number of reflections. Further, the existence of several waves in the air box at any given moment and not in phase with each other would mean that the fluctuation of pressure would be destroyed to a greater or lesser degree, owing to the coincidence of the condensation of some waves with the rarefactions of others resulting in a much reduced amplitude of pressure variations. The formula for ascertaining the frequency of pulsation can be obtained in the following way :If the length of the air box he 1 foot and the velocity of sound in air at the temperature existing in the box be 1: feet per minute, the time for a compression wave to travel from the pulsator to the opposite end of the air box and to return to the pulsator will be r of a minute. If the wave makes-n returns before the pulsator opens, the time that elapses will be e n X v of a minute. Hence the plied after every of a minute, that is they must occur at the rate of i per minute. This defines the frequency of pulsation if reinforcement is to take place after every nth return. The whole number 'n ration of the pressure impulses are also important factors. The most advantageous results in practical operation have been obtained with a,pulsator device providing a series of valve openings disposed in an end Wall of the air box or chest and embodying a series of valve members operating to mask and unmask such openings at intermittent intervals. The valve device may be of hit and miss, rotary vane, oscillatory flap, or lift type, and operated by any suitable means such as by toothed gearing or cams, and the pulses must be apnearer the construction of the pulsator can be brought in practice to present a plane surface at right angles to the waves reflected taneously delivered in one operation by the combined action of the fan or blower and the pulsator. However, it will have been understood that these compressive impulses are 'of a nature independent of any mean pressure above atmospheric which is required to be maintained in the air box, and consequently may be applied from a separate source. As an example of how this may be done reference is directed to the construction of apparatus with diaphragm or piston form of pulsator hereinafter described. i

In. order to enable the invention to be readily understood reference is directed to the accompanying more or less diagrammatic drawings in which Figure 1 is a view in longitudinal section of a construction of separating apparatus comprising a diaphragm or piston form of pulsator.

Figure 2 is a transverse section on the line IIII of Figure 1.

Figure 3 is a view similar to Figure 1 of an apparatus comprising a rotary shutter form of pulsator.

'Figure 4 is a like view of a separating apparatus with a multiple valve construction of pulsator.

Figure 5 is a section on the line V-V of Figure 4 and I Figures 6 to 8 are illustrative of further forms of pulsator.

In the drawings, the construction of the separating table or deck a is not fully illustrated as it is intended to be the same as that described in the specification accompanying my prior patent application Serial No. 277,771 filed 14th May, 1928, to which reference may be had for fuller details. It may, of course, be of any suitable constructionand further examples are given in the specification accompanying my prior patent specification Serial No. 186,474 aforesaid. In each figure of the drawings the table is shown vibratory. It is suspended from suitable supports (not shown) by spring steel hangers b and may be vibrated in 'known manner by eccentric connected with the rod 0. d represents a feed device for supplying the materials to the table.

In accordance with this invention and referring first to Figures 1 and 2, the air box 6 over which the table or deck a is mounted is made rectangular in shape in longitudinal section and is of substantially uniform cross sectional dimensions throughout its length.

The transverse section is also rectangular but this is not essential as other forms may be adopted so long as the effects sought are not interfered with. The axis of the air box is parallel, or approximately so, to the pervious parts a of the table or deck.

The pulsator device, for setting up the compressive impulses of the nature afore said, in this construction takes the form of a V diaphragm or piston f, situated at one end, preferably the rear end, of the air box and adapted to be vibrated by an eccentric 9 through the connecting rod h and piston rod is which are pivotally connected at Z. 'm, represents a guide for the piston rod. The diaphragm or piston f is constituted by a sheet of rubber or other flexible material a extending across the whole end section of the air box and held between two sheets 0 of aluminium or other suitable material. In this Way a piston may be provided having a plane area equal, as nearly as possible, to the area of the end of the box.

The apparatus also comprises a fan or blower p with delivery control valve 2' for delivering a steady or mean pressure of air to the air box e by duct 9 and through a comparatively finely perforated plate 7' constituting the bottom of the air box. The object of the plate is to give uniform entry for the air over the whole bottom of the air box.

In operation, a steady supply of air suflicient to maintain in the air box 6 a desired mean pressure issupplied by the fan p and admitted through the perforations of the plate T at the bottom of the box and during vibration of the table, the piston or diaphragm f is reciprocated. The result of this is to set up fluctuations of pressure in the air box and by operating the diaphragm with a frequency directly related to the length of the air box, waves of pressure may be superimposed upon reflected waves so as to build up fluctuations of high amplitude in the manner above described. The resistance of the perforated plate 1' would, of course, be such that the oscillating pressure would not pass it to any detrimental extent. It will be I seen that the end of the air box opposite the pulsator is of plane form placed at right angles to the direction of propagation of the waves so that the most favourable reflection of the waves towards the pulsator is obtained. The plane form of the pulsator which is disposed at right angles to the .direction of travel of the waves, is also of advantage in setting up plane waves which are reflected without distortion. The effect obtainable With this arrangement is the well known one of resonance and the intensity of the compression is determined by the displacement of the piston or diaphragm f wit-h relation to the length of the air box e.

With this construction of apparatus, the displacement of the piston or diaphragm wave, because the piston cannot pause in be-,

tween the vibrations to allow of thesuccesslve reflections.

oscillating air. If, however, a suitably shaped cam were employed, instead of an eccentric for operating the piston or dia-,

phragm, the waves could be reinforced on the second or some return thereof, other than the first, as will be readily understood.

In the construction of apparatus shown in Figure 3, a rotary shutter form of pulsator is used of similar construction to that described in the specification of any prior patent application Serial No. 186,474;\ aforesaid. There are two shutter vanes t mounted on discs at either end of the pulsator shaft u and the pulsator casing is connected with the air box proper e by a taper part c. The fan or blower for supplying the air under pressure is shown at p and it may have a delivery control valve 2' as before. In this construction, the air box 6 is of similar construction to that previously described excepting that the taper part 4; really constitutes an extension of it; The object of this taper part '0 is to enable sharper impulses'to be delivered by this type of pulsator, which cannot otherwise be obtained therewith There would be slight distortion of the waves reflected from the far end of the air box but as the taper is only slight and regularly formed and owing to the fact that reflected waves are reinforced at this end by fresh impulses deliveredby the pulsator, adverse efiects are very slight and constructions such as this have been observed to operate with almost true resonance and certainly with highly efficient stratifying action.

According to the construction of apparatus shown in Figures 4: and 5, the pulsator comprises a multiple rotary vane form of valvedevice w placed at the rear end, and in fact forming that end of the air box 0 which is of similar construction to that described with reference to Figures 1 and 2. The fan or blower p with valve 2' is similar to that seen in Figures 1 and 3. The valve device 10 comprises a flat frame y formed to provide a number of slot openings .02 extending horizontally across the whole width of the air box and in these slots is mounted a series of rotary vanes 1. The slots at are disposed as close together as possible, consistent with the strength. necessary in the intermediate valve frame parts 2, so as to allow the compressive impulses to be delivered; as nearly as possible, over the whole area of the end of the box and reduce Thefrequency of the piston; must, therefore, be the same as that of the distortion to a minimum. Taper slats 2a may be provided at the fan side of the bars 2 gearing which does not need to be shown.

In the construction shown in Figures 3 to 5 the air is supplied by the fan entirely through the pulsator but it will be understood thatif necessary a suitable mean pres sure may be supplied to the air box as well,

for example, through the bottom of the air.

box as in Figures 1 and 2.

The construction of pulsator illustrated in Figures 4 and 5, presents an advantage over, that in Figure 3, in that it enables the air box to be more truly rectangular, .the tapered part in Figure 3, constituting an extension of the air box, being eliminated in Figure 4, because the pulsator is disposed over the whole ofone end of the air box. The advantage which it presents over the diaphragm type shown in Figure 1- is that it is of more robust construction. The substantially plane form of the valve device 20, the large area of opening provided by the slots a: and the sharp cutin and cut-01f of the air attainable by the I use of the vanes ,1 permits conditions of operation corresponding-practically with complete resonance.

The modified form of pulsator shown in Figure 6 comprises a series of flat valves 2 mounted one above another across the otherwise open rear end of the air box e and adapted to oscillate in the manner of louvers. convenient mechanism for operatin the valve flaps comprises arms 3 on the spindles of the valves and; a slider 41: operated by a cam 5 and provided with pins engaging slots in the arms 3 as shown. The return or closing movement may be effected by the spring 6. It is found in this construction that very sharp opening and closing of the valves is possible and'the fiat surface presented by the valves .2 when closed gives very true reflection of pressure waves.

In Figure 7, a hit and miss form of pulsator is shown comprising a fixed valve member 7, with horizontal openings 8 which extend across the full width of the air box 6, and a reciprocating shutter 9 adapted for operation by cam 10, lever 11, and spring 12, to uncover and cover the openings 8 in a manner which will be readily understood.

Figure 8 illustrates a lift-valve form of pulsator comprisin a number of lift valves 13, mounted in guides 14 on a partition or wall 15 extending across the rear end of the air box 6. The valves may be of disc form distributed as closely as possible 'over. the area of the rear end of the wall 15 or they I in Figures 6 to 8, butit would be of similar;-

- fying said waves periodically after selected may be of plate form extending across the rear end of the. air box. They may be connected with vertical bars 16 and opened by cams 17 and closed by springs 18, or other means may be adopted for theiroperation so as to give the desired quick opening .and'closing of the valves.

The air box has not been completely shown form to that described with reference to Figures 1 and 2 or A and 5. Likewise the fan is not shown as it will be obvious how it is connected with the air box.

The air box instead of being of the kind connected with a pressure supply as above described may also be of the kind which is arranged above the bed and connected with an exhaust device or fan. In each case, it is possible to bring about fluctuation of pressure as referred to by the use of the pulsator.

I claim 1. Process for the separation of solid materials of different specific gravities, com prising forming a bed '-with the materials and distending this bed, to cause the portions of different specific gravities to stratify, by pneumatic pressure applied in a series of synchronous superposed waves.

2. Process for the separation of solid materials of different specific gravities, con1 prising forming a bed with the materials and distending this bed, to cause the portions of different specific gravities to stratify, by applying to said bed pneumatic pressure waves in a chamber and reflecting the waves back and forth in said chamber and ampli- I reflections.

3. Process for the. separation of solid materialsfof diiferent specific gravities, comprising forming a bed with the materials and distending this bed, to cause the portions of different specific gravities to stratify, by pneumatic pressure applied in a series of synchronous superposed waves together with a mean pneumatic pressure supplied independently of said waves.

4,. Process for the separation of solid materials of different specific gravities, comprising forming a bed with the materials and distending this bed, to cause the portions of diflerent' specific gravities to stratify, by static pneumatic pressure applied in a series of synchronous superposed waves.

5. Process for the separation of solid materials of diflerent specific gravities, com prising forming a bed with the materials and distending this bed, to cause the portions of difierent specific gravities to stratify, by applying to said bed waves of static pneumatic pressure in a chamber and refle ting the pressure waves back and forth in said chamber and amplifying said waves periodically after selected reflections.

6. Process for the separation of solid materials of diiferent specific gravities, comprising the formation of a bed with the materials and the distension of this bed by pneumatic pressure set up by supplying impulses of pressure beneath the bed, reflecting such impulses back and forth along the bed, and

amplifying said impulses periodically after selected reflections. I

8. Process for the separation of solid ma terials of different specificgravities, comprising the formation of a bed with the materials'and the distension of this bed by static pneumatic pressure set up by supplying impulses of pressure beneath the bed, reflecting such impulses back and forth along the bed,

and amplifying said impulses periodically after selected reflections.

'9. Apparatus for the separation of solid materials ofdiflerent specific gravities, comprising a pervious deck, a pneumatic chamber of substantially rectangular form in longitudinal section and of approximately uniform cross-section, and a pulsator device at one end of the chamber, the other end of the latter opposite the pulsator device, being of plane form and disposed at right angles to the direction of travel of the pressure waves propagated by said pulsator device, and the latter being adapted for operation at a frequency bearing such relation to the length of the chamber that synchronous amplification of all or selected pressure waves is attained.

10. Apparatus for the separation of solid materials of different specific gravities, comprising a pervious deck, a pneumatic chamber of substantially rectangular form in longitudinal section and of approximately uniform cross-section, a pulsator device at one end of the chamber and means for delivering gaseous fluid to the chamber to set up" a mean pressure independent of the impulses due to the pulsator.

11. Apparatus for the separation of solid materials of diflerent specific gravities, comprising a pervious deck, a pneumatic chamber extending along said deck, and a pulsator device disposed across one end of the chamber and embodying a series of valve members distributed over substantially the Whole area of the vertical cross-section of said chamber.

12. Apparatus for the separation of solid materials of different specific gravities, comprising a pervious deck, a pneumatic chamber, and a pulsator device disposed across one 7 end of the chamber and embodying a series of rotary valves distributed over substantially the whole area of such end of said chamber. 13. Apparatus for the separation of solid materials of different specific gravities, comprising a pervious deck, a pneumatic chamber of substantially rectangular form longitudinal section and of approximately uniform cross-section and a pulsator device disposedcat one end of thegchamber and embodying a series of rotary valves adapted to present openings extending substantially over the whole area of such end of the chamber. 14. An apparatus for the separation of solid materials of difi'erent specific gravities,

comprising a pervious deck, a pneumatic chamber of substantially rectangular form in longitudinal section and of approximately uniform cross section, one end wall of said chamber being of plane form and disposed at right-angles to the side Walls of said chamber, and a pulsator device comprising a valve movable in relation to a port opening into the other end of said chamber and adapted for operation at a speed bearing such rela-- tion to the length of the chamber that synchronous amplification of all or selected Waves setup by the pulsator is attained.-

15. Apparatus for the se aration of solid materials of different speci c gravities, comprising a pervious deck, a pneumatic chamber of substantially rectangular form in longitudinal section and of approximately uniform cross-section, and a pulsator device arranged at one end of said chamberand comprising a piston or diaphragm.

16. Apparatus for the separation of/ solid materials of different specific gravities, comprising a pervious deck, a pneumatic chamber substantially of rectangular form in longitudinal section and of approximately uni form cross-section, a piston form of pulsator at one end of the chamber and means for delivering gaseous fluid to said chamber to set up a mean pressure independently of. the i-mpulses due to the pulsator.

' GEORGE RAW. 

